United States second rower Mark Cantoni has been ruled out of the World Cup with a broken arm.
The Australia-born forward suffered the injury in the Tomahawks' shock 22-18 friendly victory over France in Toulouse.
Tomahawks coach Terry Matterson said: "Mark's been working for two years to get this opportunity so it's disappointing for him. Hopefully we may be able to get him a run at the back end, that's how keen he is."
Meanwhile former Hull KR forward Clint Newton, Wigan's new signing Eddy Pettybourne and former Castleford utility back Ryan McGoldrick have all joined up with the squad following its arrival in England.
"I've got a couple of selection headaches," said Matterson, whose side open their World Cup campaign against the Cook Islands in Bristol on Wednesday week.
Matterson is keen to play down the prospects of the tournament's 1,000-1 outsiders after they stunned the Catalan-dominated French in last Friday's warm-up fixture.
"It was a bit of a shock to the system for some of the guys playing at that level against guys that big, strong and fit but I think they showed they can handle that," he said.
"The challenge is to replicate that in a World Cup game."